Implantable cardiac stimulation devices, particularly pacemakers and implantable cardioverter defibrillators (ICDs), are usually configured to be used in conjunction with an external programmer that enables a physician to program the operation of an implanted device to, for example, control the specific parameters by which the pacemaker detects arrhythmia conditions and responds thereto. For instance, the physician may specify the sensitivity with which the pacemaker or ICD senses electrical signals within the heart and also specify the amount of electrical energy to be employed in pacing pulses or defibrillation shocks. Another common control parameter is the A-VP delay, which for dual chamber devices specifies the time delay between a paced or sensed (i.e. native) atrial event and a paced ventricular event. Additionally, the external programmer may be configured to receive and display a wide variety of diagnostic information detected by the implantable device, such as intracardiac electrogram (IEGM) signals sensed by the device, as well as diagnostic data from other sources, such as surface electrocardiogram (EKG) devices.
Herein, “A” is generally used to refer to atrial events, whether paced or sensed. “V” is used to generally refer to ventricular events, whether paced or sensed. In circumstances where it is necessary to distinguish between paced and sensed events, an “S” or “P” is appended. Hence, AS refers to a sensed atrial event, whereas AP refers to paced atrial event. VS refers to a sensed ventricular event, whereas VP refers to a paced ventricular event. A-VP represents the delay between either a paced or sensed atrial event, and a paced ventricular event. In addition, where appropriate, an “L” or “R” subscript is employed to distinguish between the left and right chambers of the heart. For example, APR refers to a paced event in the right atrium. VSR refers to a sensed event in the right ventricle. Hence, APR-VSR represents the delay between a paced event in the right atrium and a sensed event in the right ventricle. Sensed events are also referred to herein as depolarizations as they are representative of electrical depolarization of myocardial tissue. Paced events are also referred to herein as evoked responses. Paced events in the atria are triggered by A-pulses. Paced events in the ventricles are triggered by V-pulses. Finally, the term “intrinsic delay”, as used herein, refers to the delay between a paced or sensed event in one chamber and a subsequent depolarization in another chamber. For example, an “intrinsic atrioventricular delay” refers to the delay between a paced or sensed atrial event and a subsequent sensed ventricular event, e.g. an AS-VS or AP-VS delay. An “intrinsic inter-atrial delay” refers to the delay between a paced or sensed event in one atrial chamber and a subsequent sensed event in the other atrial chamber, e.g. an ASR-ASL or APR-ASL.
For many patients, particularly those with congestive heart failure (CHF), it is desirable to identify a set of control parameters that will yield optimal cardiac performance (also referred to as hemodynamic performance). Cardiac performance is a measure of the overall effectiveness of the cardiac system of a patient and is typically represented in terms of stroke volume or cardiac output. Stroke volume is the amount of blood ejected from the left ventricle during systole in a forward direction. Cardiac output is the volume of blood pumped by the left ventricle per minute (or stroke volume times the heart rate). In view of the importance of maintaining optimal cardiac performance, especially for patients with compromised cardiac function, it would be desirable to provide improved techniques for use with pacemakers or ICDs for identifying pacing control parameters that optimize cardiac performance, particularly to reduce the degree of heart failure and valvular regurgitation. It is to this end that aspects of the invention are generally directed.
It is particularly desirable to identify A-VP delay values providing the best cardiac performance. In normal patients, the electrical conduction through the AV node is intact, and the body automatically adjusts the delay via the circulating hormones and the autonomic nervous system according to its physiologic state. It is well known, for example, that in normal patients the intrinsic AS-VS delay shortens with increasing heart rate associated with a physiologic stress such as exercise. For patients with abnormal AV node conduction or complete heart block, a pacemaker can control the A-VP pacing delay by delivering a ventricular pacing pulse at a software-controlled delay after an atrial pace or atrial sensed event. Since the optimum A-VP delay varies from person to person, this parameter should be optimized on an individual basis.
Conventionally, the physician attempts to program the A-VP delay (or other parameters) for a given patient by using an external programmer to control the device implanted within the patient to cycle through a set of different A-VP delay values. For each value, the implanted device paces the heart of the patient for at least a few minutes to permit hemodynamic equilibration, then the physician records a measure of the resulting cardiac performance, measured, for example, using Doppler echocardiography. The A-VP delay value that yields the best cardiac performance is then selected and programmed into the device. However, this is a time consuming and potentially expensive procedure. As a result, some physicians do not bother to optimize A-VP delay in many of their patients. Rather, A-VP delay is merely set to a default value and is adjusted only if the patient does not respond well to pacing therapy or complains that they do not feel well. Hence, many patients are not paced at their particular optimal A-VP delay value and thus do not obtain the maximal potential benefit from the improved cardiac performance that could be gained with the optimal A-VP delay. Moreover, even in circumstances wherein A-VP delay is optimized by the physician using, for example, Doppler echocardiography, the time and associated costs are significant. In addition, the optimal A-VP delay for a particular patient may change with time due to, for example, progression or regression in CHF, changes in medications, and/or changes in overall fitness. However, with conventional optimization techniques, the A-VP delay is re-optimized, if at all, only during specially scheduled follow-up sessions with the physician to allow access to the noninvasive testing equipment such as Doppler-echocardiography, which may be months or perhaps years apart.
Accordingly, it is would be highly desirable to provide improved techniques for more easily and reliably determining optimal or otherwise preferred A-VP delay values for a particular patient. At minimum, such techniques should be designed so as to be performed by an external programmer using only IEGM data received from the implanted device along with otherwise routine surface EKG data, so that Doppler echocardiography or other expensive and time consuming cardiac performance monitoring techniques are not required. Moreover, depending upon the implanted device and its leads, the improved techniques should be designed so as to be performed by the implanted device itself, without even surface EKG data. The latter technique would permit the optimal A-VP delay to be frequently and automatically updated so as to respond to changes within the patient. It is to these ends that aspects to the invention are more specifically directed.
Note that some techniques have been proposed for determining an optimal A-VP delay value based on IEGM data. For example, it has been proposed that the A-VP delay be set to A-VP=0.7 A−VSR−55 ms. Although this allows the A-VP pacing delay to be set automatically by the implanted device, it is not believed that the formula reliably provides the optimal delay value for many patients. In particular, the formula only takes into account the intrinsic delay from the atria to the right ventricle (A-VSR) but does not take into account the intrinsic inter-atrial delay or the intrinsic delay from the atria to the left ventricle, which the present inventors believe can significantly affect the optimal A-VP delay in at least some patients. In addition, it is desirable to separately determine optimal delay values for paced and sensed events, i.e. separate values for AS-VP and for AP-VP. Accordingly, still other aspects of the invention are directed to providing improved optimization techniques that take into account intrinsic inter-atrial delay, intrinsic delay times to both the left and right ventricles, and which provide separate optimal delay values based on paced and sensed atrial events.